The present invention relates generally to fuel cells, and more particularly to fuel cells fabricated by chemical/mechanical planarization (CMP).
Fuel cells use an electrochemical energy, conversion of hydrogen and oxygen into electricity and heat. It is anticipated that fuel cells may be able to replace primary and secondary batteries as a portable power supply. In fuel cells, the fuel (containing a source of hydrogen) is oxidized with a source of oxygen to produce (primarily) water and carbon dioxide. The oxidation reaction at the anode, which liberates electrons, in combination with the reduction reaction at the cathode, which consumes electrons, results in a useful electrical voltage and current through the load.
As such, fuel cells provide a direct current (DC) voltage that may be used to power motors, lights, electrical appliances, etc. A solid oxide fuel cell (SOFC) is one type of fuel cell that may be useful in portable applications.
Unfortunately, the material properties, which are generally desirable in order to obtain high performing fuel cell devices, also make fabrication of those fuel cell devices a significant challenge.
Thin film ceramic patterning is a fairly new application. Many of the possible solutions involve thin film integrated circuit techniques that may not be well suited for refractory, generally dense metal oxide films. Some examples of patterning processes and drawbacks associated therewith include the following. With wet etching, it is very difficult to identify highly selective etchants. In plasma/dry etching (ion milling), there is often undesirable redeposition of material on sidewalls. The redeposited materials may be an undesirable phase, may adversely affect stoichiometry, and/or may make inappropriate electrical connections. Plasma etching is also relatively slow with generally no selectivity. Lift off masking is not able to withstand high temperature sintering. Further, the lift-off mask generally leaves a shadow after deposition (i.e. the deposition is non-continuous). No patterning, i.e. coating porous substrates with anode on one side and cathode on the other, greatly limits the architectures available. Shadow masking may leave particulates behind, and is rather limited in geometry resolution, for example, deposited layers generally cannot be under about 100 microns–150 microns in minimum feature size.